Dynamic and atypical E-cadherin-based attachments mediate melanoblast migration through confined epithelial spaces.

Epithelial tissues are populated with accessory cells such as immune cells, sensory cells, and pigment-producing melanocytes, which must migrate through and intercalate between tightly adherent epithelial cells. Although much is known about how cells migrate through interstitial spaces consisting of predominantly of collagen-rich ECM and mesenchyme, how cells migrate through confined epithelial spaces without impairing barrier function is far less understood. Here, using live imaging of the mouse epidermis, we captured the migration of embryonic melanocytes (melanoblasts) while simultaneously visualizing the basement membrane or epithelial surfaces. We show that melanoblasts migrate through both basal and suprabasal layers of the epidermis and hair follicles where they use keratinocyte surfaces, as well as the basement membrane, as substrates for migration. We show that melanoblasts form atypical and dynamic E-cadherin based attachments to surrounding keratinocytes that largely lack the cytoplasmic catenins known to anchor E-cadherin to the actin cytoskeleton. We show E-cadherin is needed in both melanoblasts and keratinocytes to stabilize migratory protrusions, and that depleting E-cadherin in melanoblasts results in reduced motility and ventral depigmentation in adult mice. These findings illustrate how migratory cells co-opt the cell-cell adhesion machinery connecting adjacent epithelial cells to invade between and migrate through them without interrupting the skin barrier.